1. Field Of The Invention
The invention relates generally to transmitting and receiving data of underground activity, and more specifically, data communication between a surface transmitter/receiver and underground electronic instruments such as sensors for detecting the position and status of underground drilling equipment.
In a down-hole well bore, a drill string may include an instrument package near the drill bit end to monitor the position and condition of the underground portion of the drilling equipment during operation. Data generated by the instrument package is transmitted to the surface for use by the operator.
2. Description of the Prior Art
There are several known ways to transmit data from an underground device. In a so-called wire-line configuration, data from the instrument package is transmitted through an electrical wire that runs from the instrument package through the drill string to a receiver on the surface. The wire may be a single conductor that uses the drill string as a return path or a two-conductor wire, such as a coaxial cable. The wire may be used to provide power to the instrument package from a power supply on the surface. Typically, a data rate of at least about 1200 bps (bits per second) may be achieved.
Among other disadvantages, however, the wire-line configuration is particularly vulnerable to failure of the electrical wire connection. The wire must be carefully handled during installation and operation of the drilling equipment to prevent the wire from becoming entangled or severed. Moreover, the wire may be subject to damage due to torque, vibration, repeated bending and twisting, and other mechanical forces associated with the operation of the drilling equipment. In addition, the wire-line configuration may require rotary electrical connections, which tend to reduce reliability.
Another conventional method, mud pulse telemetry, relies on modulation of the mud flow through the drilling equipment. During drilling operations, mud, or drilling fluid, is circulated through the well-bore. A mechanism positioned near the end of the drill string modulates the mud flow by opening and closing an aperture. The modulation in the mud flow is detected by a mechanical sensor at the surface.
Since mud pulse telemetry does not require a wired connection between the instrument package and the receiver through the drill string, it avoids many of the problems associated with the wire-line configuration. However, mud pulse telemetry has a data rate of only 1-2 bps. Moreover, the technique requires mechanically moving parts, which reduces reliability.
Another conventional method uses a wireless or electromagnetic (EM) configuration in which data from the down-hole instrument package is transmitted as electromagnetic signals or pulses. The instrument package includes a power source that applies a voltage across an insulated gap, thereby generating an electromagnetic field. The gap is typically a few thousandths of an inch wide and may be formed, for example, by providing an insulated coating on the treads of a connection between two sections of the drill string. The EM pulses are transmitted through the resistive soil surrounding the drilling equipment and received by a receiver on the surface.
Since the EM configuration, like mud pulse telemetry, does not require a wired connection between the instrument package and the receiver through the drill string, it avoids many of the problems associated with the wire-line configuration. However, there are number of disadvantages associated with the EM configuration.
For example, because the battery power source used to power the generation of the EM pulses is located in the underground portion of the drilling equipment, rather than on the surface, it is not readily accessible for recharging or replacement. Moreover, the batteries for the power source add to the size and weight of the instrument package.
In addition, transmitting EM pulses through soil generally requires more power and has a much lower data rate than transmission through an electrical wire. Systems employing the EM configuration typically achieve data rates of only about 5-20 bps. This is particularly disadvantageous in view of the size and weight limitations imposed on the power source by practical considerations.
The need exists for an improved system of transmitting data from underground activities.
It is a general object of the present invention to provide a data communication system for communicating with an underground electronic device that overcomes the disadvantages of conventional wire-line and electromagnetic systems.
It is another object of the present invention to provide a data communication system that does not require a wired connection that may be entangled or severed by the drilling equipment or may be vulnerable to failure due to mechanical forces associated with the operation of the drilling equipment.
It is another object of the present invention to provide a data communication system in which the communication power supply is located on the surface rather than in the underground portion of the drilling equipment, so that it is readily accessible for recharging or replacement and does not add to the size and weight of the underground electronic device.
It is another object of the present invention to provide a data communication system having a data rate comparable to or exceeding those of conventional wire-line systems.
In accordance with the objects described above, one aspect of the present invention provides a data communication system for communicating with an underground instrument package positioned on a drilling apparatus. The drilling apparatus has an insulated section between first and second conductive sections. The data communication system includes a power supply connected to the first conductive section of the drilling apparatus and to the ground. A receiver is connected to measure current flowing through the power supply. An electrical path is provided between the first and second conductive sections of the drilling apparatus. A switch opens and closes the electrical path in response to data generated by the instrument package.
Another aspect of the present invention provides a data communication system for communicating with an underground electronic device. The data communication system includes a first conductive section, a second conductive section that is positioned underground and electrically connected to the electronic device, and an insulated section positioned between and connecting the first and second conductive sections. A power supply is connected to the first conductive section and to the ground. A receiver measures current flowing through the power supply. A switch is provided in an electrical path between the first and second conductive sections. The switch opens and closes the electrical path in response to data generated by the electronic device.
Another aspect of the present invention provides a data communication method for communicating with an underground instrument package positioned on a drilling apparatus. The drilling apparatus has an insulated section between first and second conductive sections. The data communication method includes the step of connecting a power supply to the first conductive section of the drilling apparatus and to the ground. Current flowing through the power supply is measured using a receiver. A switch provided in an electrical path between the first and second conductive sections of the drilling apparatus is opened and closed in response to data generated by the instrument package.
Aspects of the present invention may include one or more of the following features.
The switch may include a transistor, such as a field effect transistor. The switch may apply frequency shift keying modulation to the current in the electrical path.
An internal power source of the instrument package may be charged by a voltage formed between the first and second conductive sections of the drilling apparatus while the electrical path is opened by the switch.
The electrical path may include a wire running through the insulated section of the drilling apparatus. An end of the wire may be connected to the first conductive section of the drilling apparatus.
The switch may be electrically connected to a conductive housing of the instrument package, and the housing of the instrument package may be electrically connected to the second conductive section of the drilling apparatus.
The power supply may be connected to the ground through a wire inserted in the ground above the underground instrument package. The instrument package may include sensors for detecting a status of the drilling apparatus.
The data communication system also may include a control transmitter for superimposing a control signal for controlling the instrument package on the current produced by the power supply. A control receiver in the instrument package may receive the control signal and generate control data in response to the control signal. The control transmitter may employ frequency shift keying.
The instrument package may activate a low power consumption mode for the internal power source in response to a switching off of the power supply. The instrument package may activate a low power consumption mode for the internal power source in response to the control data.